Various types of valve arrangements have been used where a change in the output control pressure of the fluid is supplied to an actuator, such as a clutch or a brake mechanism in an automatic transmission. Two-stage valves have been used in an effort to amplify the flow capacity as a function of a relatively small change in the input flow signal. In general such arrangements have been spool-type valves, with an orifice in the center portion where the main amplification is provided. Different types of arrangements have been used for the first of the two stages. One known approach includes the use of a servo valve, of the type wherein an electrical input signal provides a displacement of some valve component in a precise manner. However such valves are very expensive, and this militates against their use in automotive applications where cost of each component is a very significant factor.
It is therefore a primary object of the present invention to provide an improved control system for regulating actuators such as those used in the changing of gear ratios in an automatic transmission.
A corollary object is to provide such a control system which provides the advantages of a type 1 servo system but does not require an expensive valve such as a servo valve.
Another important object of the invention is to provide such a control system in which the valve spool has a less critical relationship with the valve body than is normally found in such units.